The variety and use of electronic devices, especially portable electronic devices such as cellular telephones, laptop computers, and personal digital assistants (PDAs), has dramatically increased in recent years. Many electronic devices, in addition, communicate with other electronic devices. For example, cellular telephones use base stations to rout and amplify data transmission. When designing electronic devices involved in communication, various considerations are taken into account.
One such consideration is power consumption. In most communication applications, signals are provided to a power amplifier used to amplify the signals before supplying the signals to a load. The data is modulated and up-converted from base-band (DC) into a higher, radio frequency (RF) signal. The up-converted signal is then amplified and transmitted to a desired location where the RF signal is received, and down-converted to the original signal in a receiver.
In digital applications, the data supplied to the power amplifier are square wave signals. Square wave signals are more power efficient than analog signals. Unfortunately, when modulating the signals to produce the square wave signals in the frequency band of interest, large signals (tones) are created that are outside the frequency band of interest. Generating and amplifying these tones consumes excess power. Moreover, as the amplified signal is supplied to a bandpass filter, these tones can cause destructive resonance to occur at the power amplifier and may result in a larger, sharper and more complicated-bandpass filter to be used in the device. These problems become more pronounced as the amplification increases. Reducing the tones consequently reduces the power consumed as well as permits a smaller and cheaper bandpass filter to be used.